An Access Code is a 4-word code that is provided by your practitioner, either before your first visit (via e-mail, phone, or sms), or during your visit.
The purpose of an Access Code is to give you access to Questionnaires, Treatment Plans, Documents, Appointment history, etc.
For security reasons, is it strongly advised that you redeem your access codes as soon as you get them. Leaving an access code lying around can potentially give an unauthorized person access to your information. If you lose your access code, immediately contact your practitioner so that they can cancel it and issue you a new code.
Here are some an article which explains how you can redeem an access code, once you get one:
How To Redeem an Access Code